The following relates to systems and methods for processing physiological information. It finds particular application to detecting interchanged or misplaced ECG electrode wires from ECG information, and also contemplates correcting the ECG information.
An electrocardiogram (ECG or EKG) is a graphical representation of the electrical activity (e.g., electrical potentials/signals) of the heart used for applications such as screening and diagnosing cardiovascular disease. Such electrical activity is non-invasively measured by an electrocardiograph or other suitable electrical transducer, and the graphical representation is generated therefrom and/or by another device such as a computer. Conventional twelve lead (I, II, III, aVR, aVL, aVF, and V1-6) electrocardiographs include ten electrodes for measuring the electrical activity of the heart. Each electrode is placed on the individual at a particular location within some tolerance. From these ten electrodes, twelve leads or potential differences are measured and/or derived. The leads record the average electrical activity generated by the summation of the action potentials of the heart at a particular moment in time. Other conventional systems include three, five, fifteen, sixteen, EASI, etc. lead systems.
FIG. 3 graphically illustrates an exemplary electrode placement in a standard twelve lead system. Leads I, II and III are measured over the limbs of the body. Lead I is measured from the right arm to the left arm; lead II is measured from the right arm to the left leg, and lead III is measured from the left arm to the left leg. From the average of the limb measurements, an imaginary point V located centrally in the chest above the heart is computed. The other nine leads are derived from potential differences between V and six precordial leads V1-6 and three limb leads aVR, aVL and aVF are derived from combinations of leads I, II, and III. Each lead represents information from a different portion of the heart. The inferior leads (leads II, III and aVF) provide electrical activity reflective of the inferior wall of the heart, which is the apex of the left ventricle. The lateral leads (I, aVL, V5 and V6) provide electrical activity reflective of the lateral wall of the heart, which is the lateral wall of the left ventricle. The anterior leads, V2 through V4, represent the anterior wall of the heart, or the frontal wall of the left ventricle.
The quality of an ECG analysis depends on the placement of the electrodes and/or electrode lead wires. In addition, such placement is important because clinicians are trained to interpret ECG signals based on expected patterns. Such patterns typically are common to groups of individuals with the same disease state (e.g., no cardiac disease, ischemia, myocardial infarction, etc.). Ideally, the electrodes are placed at same anatomical locations on all patients. However, such constraints are unrealistic, if not impossible. Realistically, there is an acceptable margin of error for each electrode, and the margin may vary based on the device used to process the data and the clinician interpreting the resulting waveforms. Electrode misplacement includes any change of the electrodes and/or electrode wires outside their expected anatomical locations, including electrode wire reversal that involves interchanging of the electrode wires as they are supposed to be connected to the electrodes. Electrode wire reversal alters the shape of the graphical ECG wave. For example, it can make the electrical axis of the heart appear different from the true value.
It is postured in the literature that electrode wire reversal occurs on at least 2% of ECGs in a hospital population. Detection of a right arm—left arm interchange of wires is reliably performed using standard ECG criteria. However, detection of other electrode wire interchanges can be relatively difficult. One conventional approach to lead correction leverages the redundancy in the ECG signals to correct the reversal. With this approach, regression or other techniques are used to generate a model that predicts ECG lead signals by a linear combination of the other leads. If the predicted lead signal does not match the measured/derived lead signal, it is assumed that electrode wire reversal has occurred. All wire reversals are then applied to the ECG until the predicted lead signal matches the measured/derived lead signal. This approach can be time consuming and resource intensive.